Over the past several years, the demand for electronic devices to exhibit higher levels of performance while being made smaller in size has seen a reduction in circuit component size, an increase in density, improvements in functionality, and higher circuit component mounting densities on circuit boards. As a result, there has been an increase in the temperature of the circuit components during operation, and allowing heat to dissipate has become an issue of significant importance. Various methods have been proposed in the past as means for allowing heat to radiate, and some of these methods have already been implemented.
In JP-A-2005-93582 (patent reference 1), there is disclosed a configuration for providing a radiation board having a two-layered structure comprising a metal plate and an insulating layer, whereby heat generated by circuit components is released via the radiation board. In JP-A-06-188572 (patent reference 2), there is proposed a printed circuit board with a metal core, where a continuous hollow portion is formed in the metal core to allow exposure via a side surface of the board. The hollow portion increases the size of the area through which heat radiation occurs, and makes it possible to obtain a high heat-dissipating capacity. In JP-A-06-152080 (patent reference 3), there is disclosed a configuration wherein a heat-radiating copper block that also functions as a conducting body for mounting components is attached on a portion of an upper surface of an insulating plate and a mounting portion is formed; components that generate a high amount of heat are mounted on the mounting portion; and heat is allowed to be released.
For instances when heat must be released from circuit components, there has been adopted a method for using a printed substrate having a metallic base on which a copper foil or another metallic foil is affixed with an insulating adhesive layer interposed therebetween. The printed substrate has a plate made of copper, iron, an iron-nickel alloy, aluminum, or another metal with good thermal conductivity as a base material.
However, according to the radiating means disclosed in patent reference 1, the radiation board has a small area over which heat is radiated; therefore, the radiation efficiency is low, and the amount of heat radiated is often insufficient. The means also has a complex structure, and requires the radiation board to be manufactured as a separate component to be brought into contact with a top surface of each of the circuit components with a great degree of accuracy; therefore, problems are also presented in terms of increasing component and assembly costs.
According to the radiating means disclosed in patent reference 2, there exists a limit to the number of hollow sections provided in the metal core, and the area over which heat is radiated cannot be increased; therefore, the radiation efficiency is low and the amount of heat radiated is often insufficient. There is also a need to configure the print circuit board with the metal core so that there are two or more layers; therefore, problems are also presented in terms of increasing component and manufacturing costs.
According to the radiating means disclosed in patent reference 3, the radiating copper block is covered by components mounted on its upper surface, and its other surfaces are enclosed by a second insulating board. Therefore, problems are presented in that the radiating copper block substantially lacks a surface through which heat can be radiated, and insufficient heat is radiated. Also, there is a need to manufacture the radiating copper block as a separate component, and to form a mounting portion for mounting components on its upper surface, presenting problems of increasing component and manufacturing costs.
Also, according to the radiating means using a metal-based print board, heat generated by the circuit components is released via the metal base. Again, there is a limit to the area over which heat can be released, and there may be instances where the amount of heat radiated is smaller than desired. Therefore, the need arises to use the means alongside other radiating means, and inevitably the cost ultimately increases.